Annual report pursuant to Section 13 and 15(d)

Borrowings (Credit Facility) (Narrative) (Details)

v3.10.0.1
Borrowings (Credit Facility) (Narrative) (Details)
12 Months Ended
Apr. 05, 2018
USD ($)
May 25, 2017
USD ($)
lender
Dec. 31, 2018
USD ($)
Sep. 27, 2018
USD ($)
Dec. 31, 2017
USD ($)
Nov. 07, 2017
USD ($)
Line of Credit Facility [Line Items]            
Senior secured revolving credit facility     $ 200,000,000   $ 25,000,000  
Senior secured revolving credit facility            
Line of Credit Facility [Line Items]            
Institutional lenders | lender   17        
Maximum borrowing capacity   $ 2,000,000,000        
Letters of Credit Outstanding, Amount     $ 17,675,000      
Interest rate at period end (as a percent)     3.62%      
Unused capacity, commitment fee (as a percent)     0.375%      
Senior secured revolving credit facility | LIBOR | Minimum            
Line of Credit Facility [Line Items]            
Debt instrument interest rate     1.25%      
Senior secured revolving credit facility | LIBOR | Maximum            
Line of Credit Facility [Line Items]            
Debt instrument interest rate     2.25%      
Senior secured revolving credit facility | Secured Debt            
Line of Credit Facility [Line Items]            
Debt instrument maturity date May 25, 2023 May 25, 2022        
Increase limit $ 650,000,000 $ 500,000,000 $ 850,000,000 $ 850,000,000   $ 500,000,000
Current borrowing capacity $ 825,000,000 $ 650,000,000 $ 1,100,000,000 $ 1,100,000,000   $ 700,000,000